Where an air flow system employs supply and return ducts, and a fan system for circulating air therethrough, it is sometimes desireable to provide that the direction of air flow can be reversed so that the return ducts become the supply ducts and the supply ducts become the return ducts.
This of course can be achieved by using two fans. In the majority of cases however this is too costly. In addition, if the circulation system also incorporates some form of air treatment such as heating or cooling coils or humidifiers and the like, or electronic air cleaners then the use of two fans does not solve the problem.
Proposals have been made whereby the actual fan itself is reversable ie air can flow through the fan rotor in either direction. These systems however suffer from various technical disadvantages. In the great majority of cases, the engineering of the fan system will be such that the greatest efficiency is obtained only in a preferred direction. When the fan is reversed, there is usually a considerable loss in efficiency. In certain other circumstances, various forms of moveable baffles have been proposed so that the direction of air flow may be reversed. Again however such systems almost invariably operate at maximum efficiency only in one condition.
In the particular circumstances of the present invention, it is desirable that the volumes of air flow in either direction shall be essentially equal, so that air flows take place in either direction with equal efficiency. The present invention is particularly designed to be applied to the provision of air circulation in chambers or "ovens" used for processing meat products for example drying, smoking or chilling etc. of such products. Usually this takes place over fairly extended periods of time, for example twenty-four hours or more, at a predetermined temperature and at a predetermined humidity range within the chamber whereby the meat products are subjected to such processing under carefully controlled conditions to produce predictable results, time after time during treatment.
Such meat products are treated in fairly large batches, and it is of course desireable that all the meat products in any one batch shall be subjected to more or less precisely the same air temperature and humidity so that they are all processed simultaneously to the same extent.
For this purpose, the meat products are subjected to transverse air flow through the chamber, and the air flow through the chamber is reversed at predetermined time intervals so that all of the meat products are treated to the same extent.